The phase-stabilizing agents or additives of the present invention comprise a select group of compounds from three classes: fatty acids, dimer acids, and polyester polyols. More specifically, the phase-stabilizing agents of the present invention comprises a compound selected from the group consisting of:
(i) a saturated or unsaturated C.sub.5 to C.sub.28 fatty acid; PA1 (ii) a C.sub.20 to C.sub.54 dimer acid or trimer acid; or PA1 (iii) a polyester polyol having an average molecular weight of about 200 to about 6,500.
Compounds of the above classes have been used as additives for thermoset polyester resins and other polymer resins.
For example, U.S. Pat. No. 4,210,571 discloses compounds which are useful as "surfactant coupling agents" in the preparation of thermosetting resin compositions. The materials include carboxylic acid ester derivatives of mono-, di-, and tri-hydroxy fatty acid esters of C.sub.1 to C.sub.4 mono- and polyhydric alcohols. The patentee suggests that these agents are particularly useful in reducing the viscosity of highly-bonded filler prepolymer pastes to improve the dispersion of the filler and to promote the interaction of the filler and prepolymer so as to maintain and improve the properties of the final cured resin.
U.S. Pat. No. 4,210,572 discloses a thermosetting resin composite having an inorganic filler material and coupling agent. The coupling agents disclosed include mono-, di-, and tri-long chain fatty acid esters of C.sub.1 to C.sub.4 mono- and polyhydric alcohols and polyoxyethylene derivatives of mono-, di-, and tri-hydroxy fatty acid esters of C.sub.1 to C.sub.4 mono- and polyhydric alcohols. The patentee suggests that the coupling agent is useful in reducing the viscosity of highly loaded filler prepolymer pastes to improve the dispersion of the filler and promote an interaction between the filler and the prepolymer.
U.S. Pat. No. 4,172,059 discloses a viscosity-reducing agent comprised of an aliphatic monocarboxylic acid having at least 6 carbon atoms in the chain. The aliphatic monocarboxylic acid employed usually has at least 6 carbon atoms in the chain and is frequently a saturated or unsaturated fatty acid having from 6 to 24 or more carbon atoms in the chain. The carboxylic acids may be caproic, caprylic, capric, lauric, myristic, palmitic, palmitoleic, stearic, oleic, linoleic, linolenic, and the like.
The patentee further suggests that when used in an SMC (sheet molding composition) application where the thermoplastic is a polyalkyl acrylate or methacrylate, a viscosity-reducing agent which is an unsaturated aliphatic monocarboxylic acid of at least 6 carbon atoms is employed. Such aliphatic monocarboxylic acids are frequently an unsaturated fatty acid having from 6 to 24 or more carbon atoms in the chain and includes 9-dodecenoic, 9-tetradecenoic, palmitoleic, oleic, linoleic, linolenic, and the like, and the acid may be either straight chained or branched.
It has now been surprisingly discovered that certain additives, some of which are suggested in the art as viscosity-reducing agents, are useful in a specific SMC application as phase-stabilizing agent in spite of the fact that these compounds, in many cases, actually increase viscosity.